If you use a standard hair dye, you are more likely to develop liver disease, which could lead to arthritis, thyroid problems and gut allergies. Women, in particular, who regularly use a hair dye are 37 per cent more likely to develop the liver condition known as PBC (primary biliary cirrhosis) compared with those who don't. PBC is common among people with an auto-immune disease such as rheumatoid arthritis, thyroid problems and allergies such as celiac disease, and is an early form of liver cirrhosis, a fatal disease that's often associated with heavy drinking. But in a survey of groups of people with, and without, PBC, drinking was not an important factor. However, researchers discovered a direct link with the use of hair dyes and nail polish, both of which contain octynoic acid, and with smoking. (Source: Gut, 2010; 59: 508-512).